In a height adjustment mechanism for a vehicle seat, a brake device is used which is configured such that an output shaft is caused to rotate by a swinging-up/swinging-down operation of a lever provided at an input side thereof but is prevented from rotating when a force which is derived from the weights of the seat and an occupant seated thereon and by which the seat is biased downward is applied to the output shaft.
For example, the brake device of Patent Document 1 includes three brake shoes (brake cams) arranged circumferentially inside an outer race and an output-side rotary member arranged at radially inner sides of the brake shoes. The output-side rotary member has opposed surfaces (surfaces opposite the brake shoes) each shaped as if formed by cutting part of an outer cylindrical surface flat, such that a rotary torque inputted to the output-side rotary member causes an edge formed at an extremity of each of these opposed surfaces to contact the brake shoe and push the brake shoe radially outside, thereby producing a frictional force between the brake shoe and the outer race and stopping the rotation of the output-side rotary member.
The brake device of Patent Document 2 includes an outer race having a cylindrical inner peripheral surface, a plurality of brake shoes (clamping members) opposite to the inner peripheral surface, and an output-side rotary member (pinion with wings) arranged at inner sides of the brake shoes. Herein, two sets of the clamping members are provided along an axial direction of the pinion. To be more specific, one set of the clamping members in pair is provided at one position along the axial direction of the pinion such that a central axis of the pinion is sandwiched between the clamping members in pair and two sets (pairs) of such clamping members are arranged along the axial direction of the pinion (i.e., the total four clamping members are provided).
Two of the four clamping members (one in a first set and one in a second set) are configured to stop the rotation of the pinion in the normal direction, while the other two of the clamping members (another in the first set and another in the second set) are configured to stop the rotation of the pinion in the reverse direction.